<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="body">
    <h1>Scroll me</h1>
    <h1>Scroll me</h1>
    <h1>Scroll me</h1>
    <h1>Scroll me</h1>
    <h1>Scroll me</h1>
    <h1>Scroll me</h1>
    <h1>Scroll me</h1>
    <h1>Scroll me</h1>
    <h1>Scroll me</h1>
    <h1>Scroll me</h1>
    <h1>Scroll me</h1>
  </div>
  <script>
    document.addEventListener("scroll",function(event){
	let height = document.documentElement.getBoundingClientRect().bottom - document.documentElement.clientHeight
	if(height > 50) return
	let node = document.createElement("h1")
	node.innerHTML = '我是宋兰芝'
	body.append(node)
})

  </script>
  
</body>
</html>